Search

The high-pressure and high-temperature structural, mechanical, and dinamical stability of rhodium has been investigated via synchrotron X-ray diffraction using a resistively heated diamond anvil cell and density functional theory. The isothermal compression data have been fitted with a Rydberg-Vinet equation of state (EoS) with best-fitting parameters V 0 =55.046(16) Å 3 , K 0 = 251(3) GPa, and K 0 ′ = 5.7(2). The thermal equation of state has been determined based upon the data collected following four different isotherms and has been fitted to a Holland and Powell thermal equation-of-state model with α 0 = 3.36(7)x10 - 5 K - 1 . The measured equation of state and structural parameters have been compared to the results of ab initio simulations. The agreement between theory and experiments is generally quite good. The present results solve controversies between previous studies which reported values of the bulk modulus from 240 to 300 GPa. [ABSTRACT FROM AUTHOR]

Al–Ti–C/7075 aluminum matrix composites (referred to as 7075-ATC) containing uniformly distributed TiC particles and traces of TiAl3 particles were produced by introducing 2 wt. % Al–Ti–C master alloy through stir casting. Isothermal thermal compression behavior at 300 °C–450 °C and 0.001 s−1 to 1 s−1 strain rates was studied in a Gleeble-3800 thermal simulation tester. Peak stress is influenced by deformation temperature and strain rate, reaching its maximum at low temperatures and high strain rates. The activation energy of the final thermal deformation is 150.11 kJ/mol, attributed to particle reinforcement. A sinusoidal hyperbolic Eigen structure equation for composites considering strain compensation is developed to describe the rheological stresses in composites. Dynamic recrystallization at 450 °C and a strain rate of 0.001 s⁻1 enhances composite molding properties. After hot compression, composites exhibit higher activation energy (Q) than cast 7075 and in situ particle-reinforced 7075 due to the obstruction of dislocations by the particles, grain refinement, and pinning effect on the grains. Based on the experimental results, an intrinsic model considering strain compensation was developed to accurately predict the thermal deformation behavior. EBSD results indicated that dynamic softening primarily occurred through dynamic restitution and partial recrystallization. The efficiency of softening peaked at 39% under a strain of 0.6, deformation temperatures between 350 °C and 450 °C, and strain rates ranging from 0.0009 s⁻1 to 0.0111 s⁻1. [ABSTRACT FROM AUTHOR]

Magnesium alloys with a high volume fraction of secondary phases exhibit inferior formability. Therefore, investigating their thermal deformation characteristics is critical for optimizing thermal processing techniques. In this work, isothermal compression experiments were performed on a Mg-15Gd-8Y-6Al-0.3Mn alloy with an elastic modulus of 51.3 GPa with a substantial volume of aluminum-rare earth (Al2RE) phases. The rheological behavior and microstructural evolution of the material were systematically investigated at varying temperatures (350–500 °C) and strain rates (0.001–1.000 s−1). The calculated thermal processing diagram indicates that the unstable region gradually enlarges with increased strain, and all unstable regions appear within the high-strain-rate, low-temperature domain. The ideal thermal processing range of the alloy is 350–500 °C at strain rates ranging from 0.001 to 0.016 s−1. Particle-stimulated nucleation and discontinuous dynamic recrystallization are both verified to be responsible for the recrystallized microstructure of the alloy. The recrystallized grains exhibit a relatively random crystallographic orientation. As recrystallization proceeds, the texture gradually transitions from a typical [0001] texture in the compression direction to a random texture accompanied by decreased texture intensity. This work sheds new light on the thermo-mechanical processing of high-modulus Mg alloys, which could help design suitable processing techniques for related materials. [ABSTRACT FROM AUTHOR]

A novel Al-Cu-Ni composite, featuring Ni-Al3Ni2/Al3Ni core–shell intermetallics within its matrix produced via powder metallurgy, was subjected to isothermal compression tests at different conditions so as to garner an insight into its hot deformation behaviour. These experiments were conducted from 300 to 500 °C, with strain rates varying from 0.0001 s−1 to 0.1 s−1. It is found that the flow stress is influenced by both strain rate and temperature. As the deformation temperature reduced or the strain rates increased, the peak stress level increased. To characterize the flow stress of the composite, a sine-hyperbolic constitutive equation was developed and the calculated value of activation energy (234 kJ/mol) was substantially higher than that for the self-diffusion of pure Al. Subsequently, the strain-compensated Arrhenius model and the artificial neural network (ANN) model were developed to predict the composite flow behaviour. With a lower average absolute relative error of 2.266%, a smaller root means square error of 0.668 MPa, and a higher correlation coefficient of 0.999 than the Strain-compensated Arrhenius model, the ANN model is more predictable. The processing maps show that the ideal hot working conditions for the composite are between 400 and 500 °C, with strain rates between 0.0001 s−1 and 0.01 s−1 with an efficiency of 37%. The uneven distribution in the shape and size of Core–shell/Al3Ni intermetallic compounds influenced the flow stress curves, leading to dynamic recrystallization (DRX), followed by partial dynamic recovery (DRV), and ultimately strain hardening at 0.01 s−1 & 0.1 s−1. The occurrence of recrystallization and recovery up to a specific strain followed by strain hardening at all the deformation temperatures is a rare phenomenon and has been attributed to the structure and composition of core–shell intermetallics. The occurrence of work hardening at higher strains throughout the operational range of temperatures imparts greater reliability to structural components. [ABSTRACT FROM AUTHOR]

Isothermal constant-strain-rate compression experiments of S280 ultrahigh-strength stainless steel were conducted at 800–1150 °C, 0.001–10 s−1, and 70% height reduction. The flow stress behaviors were analyzed based on the compression data. The strain compensation Arrhenius constitutive relation, multiple linear regression constitutive relation, and back-propagation (BP) neural network constitutive relation of this alloy were established for the first time. The S280 ultrahigh-strength stainless steel is characterized by a positive strain rate and negative temperature sensitivity. Its flow stress at high temperature (1000–1150 °C) and low temperature (800–950 °C) is generally at the steady state and the softening state, respectively. The three new flow stress constitutive relations all meet the requirements for engineering applications in terms of predictive precision. The BP neural network constitutive relation shows the highest predictive precision, with correlation coefficient R of 0.999 and average absolute relative error AARE of 1.04%. The strain compensation Arrhenius constitutive relation shows the lowest predictive precision, with R of 0.994 and AARE of 14.748%. The multiple linear regression constitutive relation shows the modest predictive precision, with R of 0.994 and AARE of 6.24%. [ABSTRACT FROM AUTHOR]

In this work, the deformation behavior of Al-8.1Zn-2.0Mg-1.0Cu-0.2Ag-0.15Zr alloy was studied under isothermal compression, with strain rate and temperature in the range of 0.001 s−1−10 s−1 and 330 °C−450 °C, respectively. First, it was found that the deformation temperature significantly affected the dynamic recrystallization (DRX) and phase transformation behaviors of this alloy. At 330 °C, discontinuous dynamic recrystallization (DDRX) and arched grain boundaries were observed, whereas dislocation entanglements dominated continuous dynamic recrystallization (CDRX) was notably detected at 370 °C. Temperatures exceeding 410 °C facilitated the CDRX behavior, as polygonal chain-like subgrains and block-like dislocation loops were found within the new grains. High deformation temperatures also resulted in the amalgamation and growth of adjacent subgrains. Moreover, we found the Ag-containing phase spheroidized and grew at high temperatures, while the deformation had little effect on the Al3Zr. Strain rate also significantly affected the deformation behavior of this alloy. Samples deformed at 0.001 s−1 exhibited prolonged deformation time with clear dynamic recovery (DRV) and DRX. At 1 s−1, irregular dislocation distribution was observed, while at 10 s−1, shear band formation induced by deformation instability was evident. Furthermore, the deformation induced η′/matrix interfacial transformation from Zn clusters to a Zn–Mg common interface. Particularly, the precipitation order at grain boundary was proved to be Zn atomic clusters → Zn, Mg atomic clusters (GP zone) → η′ (MgZn2).

In this paper, isothermal thermal compression tests were carried out on Al–Zn–Mg–Cu alloys at varying deformation temperatures (360°C∼440°C) and strain rates (0.001s−1∼10s−1) using a Gleeble-3500C thermal simulation tester. Based on the true strain stress data obtained from the tests, the flow behavior of Al–Zn–Mg–Cu alloys during thermal deformation was investigated. Through a comprehensive consideration of deformation temperature, strain rate, and strain compensation, a high-precision constitutive model was established. Additionally, the specimens subjected to hot compression were further treated with solution annealing for different durations (0 h–2 h) to investigate the static recrystallization (SRX) behavior and the associated microstructural evolution of the alloy during the solution treatment process. Electron Backscatter Diffraction (EBSD) was employed to characterize the microstructure evolution of Al–Zn–Mg–Cu alloy under various deformation and solution treatment conditions. The EBSD data were further processed and analyzed using the MTEX toolbox. The results revealed that dynamic recovery (DRV) is the predominant softening mechanism during the deformation process, accompanied by a small amount of dynamic recrystallization (DRX). The dynamically recrystallized grains exhibit a random crystallographic orientation. Further investigation showed that low temperature and high strain rate conditions are unfavorable for the occurrence of dynamic recovery and dynamic recrystallization during the thermomechanical processing. However, dislocations accumulated during deformation provided sufficient stored energy for the growth of static recrystallized grains during subsequent solution treatment, with static recrystallized grains predominantly forming at grain boundaries.

Graphene/copper composites are promising in electronic and energy fields due to their superior conductivity, but microstructure control during thermal mechanical processing (TMP) remains a crucial issue for the manufacturing of high-performance graphene/copper composites. In this study, the hot deformation behavior of graphene/copper composites was investigated by isothermal compression tests at deformation temperatures of 700~850 °C and strain rates of 0.01~10 s−1, and a constitutive equation based on the Arrhenius model and hot processing map was established. Results demonstrate that the deformation mechanism of the graphene/copper composites mainly involves dynamic recrystallization (DRX), and such DRX-mediated deformation behavior can be accurately described by the established Arrhenius model. In addition, it was found that the strain rate has a stronger impact on the DRX grain size than the deformation temperature. The optimum deformation temperature and strain rate were determined to be 800 °C and 1 s−1, respectively, with which a uniform microstructure with fine grains can be obtained. [ABSTRACT FROM AUTHOR]

Herein, the hot deformation behavior of a near-α Ti-5Al-1Sn-1 V-1Zr-0.8Mo (Ti-5111) titanium alloy was studied at 870-1050 °C during isothermal compression tests at a strain rate of 0.01-10.0 s−1. The microstructural evolution mechanism in the titanium alloy was systematically analyzed. Results show that the flow stress values rapidly increase to the peak value and gradually decrease as the strain variable increases. Further, the peak stress declines with the increasing deformation temperature. The apparent activation energy values of (α + β) and β regions are 438 and 206 kJ mol−1, respectively. The variation of flow stress against temperature and strain rate is established using the constitutive equation. The safe processing zones are 890-960 °C and 960-1010 °C at strain rates of 0.01-0.3 s−1 and 0.1-2 s−1, respectively, as determined using the hot processing diagram. The maximum energy dissipation efficiency is 0.59 at 0.01 s−1 and 930 °C, which is the optimum processing technique. The flow instability for the Ti-5111 alloy will occur at a high strain rate when shear bands and microscopic cracks appear in the deformed microstructures. Therefore, processing Ti-5111 alloy in unstable zones of the hot processing diagram should be avoided. [ABSTRACT FROM AUTHOR]

The material constitutive equation of 25CrMo4 steel was established through an isothermal compression experiment. First, a thermal compression experiment was carried out with a Gleeble-3500 thermal simulator to study the thermoplastic deformation behaviour of 25CrMo4 steel at various temperatures (850, 950, 1050, and 1150 °C) and strain rates (0.01, 0.1, 1.0, and 10 s−1). The measured true stress–strain curve showed that when the temperature is constant, the flow stress increases with the strain rate, whereas when the strain rate is constant, the flow stress decreases with the temperature. Then, the constitutive model of peak stress of 25CrMo4 was established after analyzing the stress and strain statistics. The model parameters were optimized. The accuracy of the flow stress constitutive model was verified by comparing the flow stress prediction model with the experimental results. The hot forging process of the inner core wheel was numerically simulated based on DEFORM-3D v11 software, and the parameters of this process were formulated by analyzing the metal flow rate and equivalent stress and strain fields. [ABSTRACT FROM AUTHOR]

Copyright of Materials & Technologies / Materiali in Tehnologije is the property of Institute of Metals & Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The Laasraoui segmented and Arrhenius flow stress model, dynamic recrystallization (DRX) model, grain size prediction model, and hot processing map (HPM) of Fe-Cr-Mo-Mn steels were established through isothermal compression tests. The models and HPM were proven by experiment to be highly accurate. As the deformation temperature decreased or the strain rate increased, the flow stress increased and the grain size of the Fe-Cr-Mo-Mn steel decreased, while the volume fraction of DRX (Xdrx) decreased. The optimal range of the hot processing was determined to be 1050–1200 °C/0.369–1 s−1. Zigzag-like grain boundaries (GBs) and intergranular cracks were found in the unstable region, in which the disordered martensitic structure was observed. The orderly packet martensite was formed in the general processing region, and the mixed structure with incomplete DRX grains was composed of coarse and fine grains. The microstructure in the optimum processing region was composed of DRX grains and the multistage martensite. The validity of the Laasraoui segmented flow stress model, DRX model, grain size prediction model, and HPM was verified by upsetting tests. [ABSTRACT FROM AUTHOR]

Isothermal compression tests for ERNiCrMo-3 alloy specimens were conducted under temperatures of 990–1170 °C with strain rates of 0.01–10 s−1. Hot deformation behavior of ERNiCrMo-3 was analyzed based on the obtained flow stress curves. Three constitutive models were developed to anticipate the flow stress: the Arrhenius model compensated by strain, the Arrhenius model optimized by genetic algorithm (GA), and the artificial neuron network (ANN) model. The correlation coefficient (R) and average absolute relative error (AARE) were used to assess the predictive ability for these three models. The R values of the strain-compensated, GA optimized, and ANN models were 91.04, 93.54, and 99.01%, respectively, while the AARE values were 12.30, 8.19, and 2.92%, respectively. Furthermore, the absolute relative error of the ANN model was the most concentrated and mainly around 0. Therefore, the ANN model provides the maximum predictability and accuracy for flow stress. The ANN model was implemented via subroutine USRMTR in DEFORM 2D to simulate the hot compression process of the ERNiCrMo-3 alloy specimens. The numerical results were in good agreement with the experimental results, indicating a high potential for applicability to actual production processes. Finally, hot working characteristic of ERNiCrMo-3 alloy was analyzed by processing map and microstructural investigation. According to the result, the suitable thermal processing domain for ERNiCrMo-3 alloy should be at a temperature range of 1130–1170 °C and a strain rate range of 0.03–0.36 s−1. [ABSTRACT FROM AUTHOR]

The hot deformation behavior and mechanism of Ti65 alloy with a bimodal microstructure were investigated by isothermal compression experiments conducted on the Thermecmastor-Z simulator equipment at temperatures ranging from 950 to 1110 °C and strain rates ranging from 0.01 to 10.0 s−1. The Arrhenius constitutive model, based on strain compensation, and Grey Wolf optimization-neural network with back propagation model (GWO–BP), were both established. The differences between the experimental and predicted value of flow stress were compared and analyzed using the two models. The results show that the prediction accuracy of GWO–BP in the two-phase region is higher than that of Arrhenius model. In the single-phase region, both methods demonstrated high prediction accuracy. Compared to the single-phase region, the flow stress of Ti65 alloy shows a higher degree of softening in the two-phase region. During deformation in the two-phase region, the initial lamellar α phase transformed from a kinked and elongated morphology to a globularized topography as the strain rate decreased. Boundary-splitting was the primary mechanism leading to the spheroidization process. The degree of recrystallization increased with the increase in strain rate during the deformation in the single-phase region, while dynamic recovery and strain-induced grain boundary migration were the main deformation mechanisms at a lower strain rate. Discontinuous dynamic recrystallization may be the dominant recrystallization mechanism under a high strain rate of 10 s−1. [ABSTRACT FROM AUTHOR]

During thermal deformation, grain coarsening due to grain growth and grain refinement resulting from dynamic recrystallization (DRX) collectively influence the deformed grain size. To investigate the separative and comprehensive effects of the two mechanisms in the Ni-38Cr-3.8Al alloy, grain growth experiments and isothermal compression tests were conducted. Kinetics models for grain growth and DRX behaviors were established based on the experimental data, which were integrated with finite element (FE) techniques to simulate the evolution of grain size throughout the entire thermal compression process. The effects of grain coarsening and grain refinement during this process were separated and quantified based on the simulation data. The results revealed that grain coarsening predominated during the heating and holding stages, with a longer holding time and higher holding temperatures intensifying this effect. However, during the compression stage, grain coarsening and grain refinement co-existed, and their competition was influenced by deformation parameters. Specifically, grain refinement dominated at strain rates exceeding 0.1 s−1, while grain coarsening dominated at lower strain rates (<0.1 s−1) and higher deformation temperatures (>1373 K). The simulated grain sizes closely matched the experimental observations. [ABSTRACT FROM AUTHOR]

The mechanical properties of metastable β-titanium alloys are highly susceptible during the thermal mechanical processing (TMP). In this process, the recrystallization process plays an important role in determining the microstructure and texture evolution. The implementation of dynamic recrystallization (DRX), a process for achieving β-grain refinement, is considered of great significance for the improvement of the properties of metastable β-titanium alloys and their industrial production. Along these lines, in this work, an isothermal compression test of TB8 titanium alloy was carried out by using a Gleeble-3500 thermal simulator. As a result, the rheological stress behavior was analyzed, the thermal processing map was accurately established based on the stress–strain curve, and the optimal processing interval was determined. The DRX kinetic and the DRX grain size models were developed, on the basis of which a new DRX intrinsic model was established to improve the material parameters. Therefore, the actual situation in the working process could be better predicted. The microstructural evolution of TB8 titanium alloy during thermal deformation was comprehensively investigated using the electron backscatter diffraction (EBSD) technique. The obtained results demonstrate a close correlation between the diversity of DRX mechanisms in TB8 alloy and the distribution of dislocation density. Four microstructural textures during thermal deformation were identified, in which the cube texture of (001) <010> and the R-Gorss Nd texture of (110) <110> dominate. Due to the random orientation of the dynamically recrystallized grains, the strength of the R-Gorss Nd texture of (110) <110> increases with the increase in the volume fraction of DRX. On the contrary, it was verified that the dynamic recrystallization behavior has a significant weakening impact on the cube texture of (001) <010>. [ABSTRACT FROM AUTHOR]

This study investigated the formation mechanism of new grains due to twin–twin intersections in a coarse-grained Mg–6Al–3Sn–2Zn alloy during different strain rates of an isothermal compression. The results of electron backscattered diffraction investigations showed that the activated twins were primarily { 10 1 ¯ 2 } tension twins, and 60° < 10 1 ¯ 0> boundaries formed due to twin–twin intersections under different strain rates. Isolated twin variants with 60° < 10 1 ¯ 0> boundaries transformed into new grains through lattice rotations at a low strain rate (0.01 s−1). At a high strain rate (10 s−1), the regions surrounded by subgrain boundaries through high-density dislocation arrangement and the 60° < 10 1 ¯ 0> boundaries transformed into new grains via dynamic recrystallization. [ABSTRACT FROM AUTHOR]

The hot deformation behavior of Al-Zn-Mg-Cu alloy was investigated by flow stress curves in isothermal hot compression experiments with deformation temperatures of 350–450 °C and strain rates of 0.01 s−1 to 1 s−1, and the constitutive equation of homogeneous alloy was obtained. At the same time, the dynamic recrystallization and precipitation behavior during hot deformation and the relationship between them and the Z parameters were studied by using EBSD and TEM. DRV is the main mechanism of dynamic softening. With the decrease in Z parameter, the softening mechanism changes from dynamic recovery to discontinuous dynamic recrystallization or continuous dynamic recrystallization. At a higher Z parameter, the dislocation density and precipitated phase density are also higher because the high dislocation density provides heterogeneous nucleation sites of the precipitated phase. A large number of precipitates in the alloy also inhibit the nucleation and growth of dynamic recrystallization by hindering dislocation movement and grain boundary migration. [ABSTRACT FROM AUTHOR]

To obtain the optimal hot deformation process, the rheological and dynamic recrystallization behaviors of A100 steel were researched through isothermal compression tests. Firstly, a Hensel-Spittel constitutive model was established based on the stress–strain curves. Secondly, dynamic recrystallization percentage and grain size models were established to identify the necessary conditions for complete dynamic recrystallization. Finally, microstructural analysis was employed to validate the accuracy of the recrystallization model. The results indicate that the flow stress is highly sensitive to both the strain rate and the temperature, and the HS model demonstrates a high predictive accuracy, with a correlation coefficient of 0.9914. There exists a contradictory relationship between decreasing the average grain size and increasing the recrystallization percentage. The higher the percentage of dynamic recrystallization, the larger the average grain size tends to be. This situation should be avoided when devising the actual processing procedures. The optimal hot working processes for achieving complete dynamic recrystallization and a smaller average grain size are as follows: a strain equal to or greater than 0.6, a temperature between 1193 and 1353 K, and a strain rate between 0.1 and 1 s−1. [ABSTRACT FROM AUTHOR]

In this work, a new use of mixed Ti-6Al-4V powder, consisting of the retained powder after screening for additive manufacturing and the recycled powder after multiple printing, has been exploited. The powder mixture has been hot-isostatically-pressed (HIPed) at 930 °C/120 MPa for 3 h to reach full density. The hot deformation behavior of the as-HIPed powder compacts were investigated through isothermal compression tests, kinetic analyses, and hot processing maps. Finally, the optimized hot working parameters were validated using upsetting tests. The results show that the as-HIPed Ti-6Al-4V alloy has a fine and homogeneous microstructure. The activation energies were calculated to be 359 kJ/mol in the α + β phase regime and 463 kJ/mol in the β phase regime, respectively. The optimal hot working parameters are a deformation temperature above 950 °C and strain rate higher than 0.1 s−1. The hot workability of as-HIPed powder compacts is better than the as-cast billets. The deformed microstructure can be finer than that of as-HIPed state, and the mechanical performance can be further improved by the optimal thermo-mechanical processing treatment. [ABSTRACT FROM AUTHOR]

The constitutive model refers to the mapping relationship between the stress and deformation conditions (such as strain, strain rate, and temperature) after being loaded. In this work, the hot deformation behavior of a Ni-Cr-Mo steel was investigated by conducting isothermal compression tests using a Gleeble-3800 thermal simulator with deformation temperatures ranging from 800 °C to 1200 °C, strain rates ranging from 0.01 s−1 to 10 s−1, and deformations of 55%. To analyze the constitutive relation of the Ni-Cr-Mo steel at high temperatures, five machine learning algorithms were employed to predict the flow stress, namely, back-propagation artificial neural network (BP-ANN), Random Committee, Bagging, k-nearest neighbor (k-NN), and a library for support vector machines (libSVM). A comparative study between the experimental and the predicted results was performed. The results show that correlation coefficient (R), root mean square error (RMSE), mean absolute value error (MAE), mean square error (MSE), and average absolute relative error (AARE) obtained from the Random Committee on the testing set are 0.98897, 8.00808 MPa, 5.54244 MPa, 64.12927 MPa2 and 5.67135%, respectively, whereas the metrics obtained via other algorithms are all inferior to the Random Committee. It suggests that the Random Committee can predict the flow stress of the steel more effectively. [ABSTRACT FROM AUTHOR]

Engine components, particularly exhaust valves, are manufactured by a specific forming process known as electric upsetting, which contributes to microstructures with finer grains which enhance the performance of these components. To this end, it is necessarily required to describe the grain evolution behaviors of heat-resistant alloys during the electrical-thermal-mechanical coupling forming process. The grain evolution behaviors of Ni80A superalloy including dynamic recrystallization (DRX) kinetics models and mesoscale cellular automaton (CA) model are solved from the acquired stress–strain curves in resistance heating isothermal compression tests. Following which, a multi-field and multi-scale coupling FEM model is established by embedding the multi-scale grain evolution models into the electrical-thermal-mechanical multi-field coupling compression model. Then the grain evolution behaviors in isothermal compressions with processing conditions are reproduced by simulations. The results reveal that during the isothermal compressions, recrystallized grains intend to bulge and generate around the original grain boundaries, representing as 'necklace' microstructures inhomogeneously distributed in the matrix, and then such grain morphology is gradually replaced by refined and equiaxed DRX grains. For a fixed strain, grain size decreases with decreasing temperature and increasing strain rate. Finally, the EBSD characterization results show that the developed FEM model can well describe the grain evolution behaviors of Ni80A superalloy in electrical-thermal-mechanical coupling compression process. [ABSTRACT FROM AUTHOR]

Amorphous ices are usually classified as belonging to low-density or high-density amorphous ice (LDA and HDA) with densities ρLDA ≈ 0.94 g/cm3 and ρHDA ≈ 1.15−1.17 g/cm3. However, a recent experiment crushing hexagonal ice (ball-milling) produced a medium-density amorphous ice (MDA, ρMDA ≈ 1.06 g/cm3) adding complexity to our understanding of amorphous ice and the phase diagram of supercooled water. Motivated by the discovery of MDA, we perform computer simulations where amorphous ices are produced by isobaric cooling and isothermal compression/decompression. Our results show that, depending on the pressure employed, isobaric cooling can generate a continuum of amorphous ices with densities that expand in between those of LDA and HDA (briefly, intermediate amorphous ices, IA). In particular, the IA generated at P ≈ 125 MPa has a remarkably similar density and average structure as MDA, implying that MDA is not unique. Using the potential energy landscape formalism, we provide an intuitive qualitative understanding of the nature of LDA, HDA, and the IA generated at different pressures. In this view, LDA and HDA occupy specific and well-separated regions of the PEL; the IA prepared at P = 125 MPa is located in the intermediate region of the PEL that separates LDA and HDA. Recently, a medium-density amorphous ice (MDA) was synthesized via ball-milling of hexagonal ice, adding complexity to our understanding of the phase diagram of supercooled water and amorphous ice. Here, the authors use molecular dynamics simulations to show that, depending on the employed pressure, isobaric cooling can generate a continuum of amorphous ices with densities that expand in between those of low- and high-density amorphous ices, with some of these amorphous ices being remarkably similar to MDA. [ABSTRACT FROM AUTHOR]

Single-pass isothermal hot compression tests on four medium-Mn steels with different C and Al contents were conducted using a Gleeble-3500 thermal simulation machine at varying deformation temperatures (900–1150 °C) and strain rates (0.01–5 s−1). Based on friction correction theory, the friction of the test stress–strain data was corrected. On this basis, the Arrhenius constitutive model of experimental steels considering Al content and strain compensation and hot processing maps of different experimental steels at a strain of 0.9 were established. Moreover, the effects of C and Al contents on constitutive model parameters and hot processing performance were analyzed. The results revealed that the increase in C content changed the trend of the thermal deformation activation energy Q with the true strain. The Q value of 2C7Mn3Al increased by about 50 KJ/mol compared with 7Mn3Al at a true strain greater than 0.4. In contrast, increasing the Al content from 0 to 1.14 wt.% decreased the activation energy of thermal deformation in the true strain range of 0.4–0.9. Continuing to increase to 3.30 wt.% increased the Q of 7Mn3Al over 7Mn by about 65 KJ/mol over the full strain range. In comparison, 7Mn1Al exhibited the best hot processing performance under the deformation temperature of 975–1125 °C and strain rate of 0.2–5 s−1. This is due to the addition of C element reduces the δ-ferrite volume fraction, which leads to the precipitation of κ-carbides and causes the formation of microcracks; an increase in Al content from 0 to 1.14 wt.% reduces the austenite stability and improves the hot workability, but a continued increase in the content up to 3.30 wt.% results in the emergence of δ-ferrite in the microstructure, which slows down the austenite DRX and not conducive to the hot processing performance. [ABSTRACT FROM AUTHOR]

During the thermal deformation of aluminum alloy materials, the deformation conditions such as deformation volume, temperature and strain rate are important factors that influence the deformation mechanisms such as work hardening, dynamic recovery and dynamic recrystallization. Under the interaction of different deformation mechanisms, the properties of aluminum alloy materials will change significantly. In this study, isothermal hot compression experiments were conducted on the Al-7.92 Zn-1.64 Mg-2.00 Cu alloy to analyze its hot flow behavior (T = 250~450 °C, ɛ̇ = 0.001~1 s−1). The obtained flow behavior data were used to construct an Arrhenius-type constitutive equation and processing maps, investigating organizational evolution under diverse hot deformation conditions. The results show that the energy dissipation rate can reach 0.37 when the deformation temperature T = 380~450 °C and the strain rate ɛ̇ < 0.1 s−1, suggesting that the material is most suitable for thermal deformation processing at high temperatures and low strain rates. At a strain rate of 0.1 s−1 and a temperature of 450 °C, the percentage of recrystallized grains and substructures increased by 7.20% and 3.14%, respectively, compared to 300 °C, which is due to the severe dynamic recovery and dynamic recrystallization. At 350 °C and 0.1 s−1, there was a higher percentage of recrystallized grains and substructures, 5.44% and 5.87% higher, respectively, than at a strain rate of 1 s−1, indicating that the release of dislocation accumulation due to deformation storage energy will be more favored at low strain rates, which promotes the enhancement of the dynamic recrystallization mechanism. [ABSTRACT FROM AUTHOR]

The hot deformation behavior of 300M ultra-high strength steel is investigated through isothermal uniaxial compression tests under various thermo-mechanical processing conditions of 900-1250 °C and 0.01-50 s−1. Using the friction-corrected data of the experimental flow stress, the strain-compensated Arrhenius-type model, modified Johnson–Cook model and Khan–Huang–Liang model are developed. Based on the analysis of the reason of large deviation, the modified Johnson–Cook and Khan–Huang–Liang models are improved. The strain-compensated Arrhenius-type model exhibits the highest prediction accuracy. The determination coefficient and average absolute relative error of the strain-compensated Arrhenius-type model are 0.9971 and 3.57%, respectively. Meanwhile, the improved version of the modified Johnson–Cook model records the determination coefficient of 0.9964 and average absolute relative error of 3.59%, and the improved Khan–Huang–Liang model records 0.9949 and 5.08%. In view of the prediction accuracy and computation complexity, the improved versions of the modified Johnson–Cook and Khan–Huang–Liang models are preferred models. The improved phenomenological constitutive models enable us to predict the hot deformation behavior effectively for the optimization of the thermo-mechanical processing parameters of 300M ultra-high strength steel. [ABSTRACT FROM AUTHOR]

In this paper, the isothermal thermal compression simulation test of 2024 aluminum alloy was carried out. The deformation temperature is 573-723 K, the strain rate is 0.01-10 s−1, and the deformation amount is 50%. The experimental results show that the change of flow stress is inversely proportional to the deformation temperature, but directly proportional to the strain rate. OM and TEM were used to observe the microstructure after thermal deformation, the increase of temperature and the decrease of strain rate contribute to the formation of recrystallization and the decrease of dislocation density, which is the main reason for dynamic softening. The thermal deformation activation energy of 2024 aluminum alloy is 201.62 kJ/mol. The experimental peak stress constitutive model is in good agreement with the calculated value. Based on the Prasad instability model and the dynamic material model, the hot working diagram of 2024 aluminum alloy is established to construct the true strain of 50%. The ideal deformation conditions are the deformation temperature of 573-673 K and strain rate of 0.01-0.1 s−1. [ABSTRACT FROM AUTHOR]

With an aim to study the hot workability and establish the safe working zone for Ni-based superalloy XH43, cylindrical specimens were subjected to hot isothermal compression test at different temperatures (1173-1373 K) and strain rates (10−3-10 s−1) using Gleeble thermo-mechanical simulator. Strain rate sensitivity and Zener–Hollomon parameter have been calculated. Processing maps and constitutive equations have been developed and verified with the experimental results. It is observed that dynamic recrystallization (DRX) is the principal flow softening mechanism. Strain rate sensitivity obtained through constant strain rate test (CSRT) m and through cyclic strain rate jump test (CSRJT) m' is found to have close match initially up to 0.3 strain. Subsequently at higher strain m has marginal reduction, whereas m' decreases drastically to low value. This is attributed to dynamic softening at higher strain, which is predominant in case of CSRJT where cyclic test is assisting the softening process. Activation energy Q obtained through CSRT is found to be slightly higher than activation energy (Q') obtained through dynamic test like CSRJT and jump temperature test (JTT). This indicates less dragging force for deformation of alloy in dynamic tests, which is closer to industrial practice. It is also found that alloy has good workability in the temperature range of 1173-1373 K at strain rates of 0.01-0.001 s−1. In this range of parameters, the alloy follows the constitutive equation very closely. [ABSTRACT FROM AUTHOR]

The beryl-group mineral johnkoivulaite, Cs(Be2B)Mg2Si6O18, was compressed hydrostatically in a diamond-anvil cell up to 10.2 GPa. In situ Raman spectroscopy and X-ray crystallography revealed a P6/mcc-to-P 3 c1 (second-order) phase transition on isothermal compression at the critical transition pressure Pc = 4.13 ± 0.07 GPa. The elastic parameters determined for the volume elasticity of the two polymorphs correspond to a Birch-Murnaghan equation of state with K0 = 148 ± 2 GPa and K ′ = 0 for P < Pc and K0 = 75.5 ± 0.9 GPa with K ′ = 4 for P > Pc. The low-P polymorph shows anomalously linear compression behavior, as reported for several other beryl-derived framework structures. The high-P polymorph, which was found to follow a a ′ = a ⋅ 3 , c ′ = c superstructure according to P 3 c1, is almost twice as compressible as its low-P form. This is unique for any beryl-derived structure and can be attributed to the high degree of freedom for atomic displacements in the superstructure. The reduced symmetry can also be understood as the effect of the driving mechanism of the transformation. The extra-framework Cs channel components counteract any lateral deformation of the channels parallel to [0001] within the microporous framework and, similar to pezzottaite, are responsible for maintaining the trigonal/hexagonal lattice metrics. [ABSTRACT FROM AUTHOR]

Presently, mechanical system vibroisolation is becoming increasingly important. One of the new approaches is semi-active vibroisolation using elements capable of changing a selected mechanical property. These include, among others, pneumatic flexible shaft couplings capable of changing torsional stiffness during operation. The main goal of the article is to examine the potential advantages of a newly patented pneumatic coupling over a current type with the same pneumatic element arrangement. For comparison, parameters determinable from static load characteristics were selected. These parameters are maximum twist angle and torque, average torsional stiffness, and the percentage of torque transmitted by the bellows rubber shell. In all cases, the new coupling had better properties. Since the prototype of the new coupling has not yet been produced, its parameters were determined from its mathematical-physical model. The article contains a full procedure to obtain the static load characteristic of a new coupling type, beginning with the determination of air bellows force/height and volume/height characteristics, then optimum sizes of coupling with regards to the operating range of elements, the dependency of element height on the coupling's twist angle, and finally the computation of the static load characteristic considering isothermal gas compression. The presented procedure can be applied to any pneumatic bellows where the force/height characteristics of different pressures are given. [ABSTRACT FROM AUTHOR]

The beryl-group mineral johnkoivulaite, Cs(Be2B)Mg2Si6O18, was compressed hydrostatically in a diamond-anvil cell up to 10.2 GPa. In situ Raman spectroscopy and X-ray crystallography revealed a P6/mcc-to-P 3 c1 (second-order) phase transition on isothermal compression at the critical transition pressure Pc = 4.13 ± 0.07 GPa. The elastic parameters determined for the volume elasticity of the two polymorphs correspond to a Birch-Murnaghan equation of state with K0 = 148 ± 2 GPa and K ′ = 0 for P < Pc and K0 = 75.5 ± 0.9 GPa with K ′ = 4 for P > Pc. The low-P polymorph shows anomalously linear compression behavior, as reported for several other beryl-derived framework structures. The high-P polymorph, which was found to follow a a ′ = a ⋅ 3 , c ′ = c superstructure according to P 3 c1, is almost twice as compressible as its low-P form. This is unique for any beryl-derived structure and can be attributed to the high degree of freedom for atomic displacements in the superstructure. The reduced symmetry can also be understood as the effect of the driving mechanism of the transformation. The extra-framework Cs channel components counteract any lateral deformation of the channels parallel to [0001] within the microporous framework and, similar to pezzottaite, are responsible for maintaining the trigonal/hexagonal lattice metrics. [ABSTRACT FROM AUTHOR]

Measurements of the electrical resistance of shock-compressed aluminum are used in the present study to estimate the concentration of point defects generated by the shock wave front. The parameters of the physical state of a thin metal sample are found by means of modeling the shock wave processes in the measurement cell. Experimental values of the specific electrical resistance of aluminum are compared with predictions of the equilibrium electrical resistance model. The proposed model ensures an adequate description of currently available reference data on equilibrium isothermal compression and isobaric heating of aluminum. At the same time, the shock wave experiment yields a higher specific electrical resistance than that predicted by the model of the electrical resistance of an equilibrium defectless crystal. The detected difference in the specific electrical resistances testifies to generation of defects of the crystal structure of the metal subjected to dynamic compression. Under the assumption of predominant formation of vacancies, the concentration of defects in aluminum is estimated as a function of the shock wave pressure. The number of defects in the metal increases with an increase in the shock wave pressure. The data obtained are qualitatively consistent with available results for copper and silver, which allows one to claim that generation of defects under shock compression has common specific features for these metals. The physical state of shock-compressed aluminum is thermodynamically nonequilibrium and includes numerous defects. [ABSTRACT FROM AUTHOR]

The investigation of thermal deformation behavior plays a significant role in guaranteeing the overall performance of alloy materials. In this manuscript, a series of isothermal compression tests at different temperatures (300, 350, 400, and 450 °C) and strain rates (0.001, 0.01, 0.1, and 1 s−1) were conducted to study the thermal deformation behavior of 7075 aluminum alloy. Subsequently, processing maps at a strain from 0.4 to 1.39 were established according to the stress–strain data obtained from various deformation parameters. The microstructural evolution of the target alloy was observed with an optical microscope and transmission electron microscope. The results reveal the unstable regions are located at (360–450 °C, 0.04–1 s−1) and (300–315 °C, 0.01–0.22 s−1). Precipitation particles, pinned dislocations, and highly dislocated areas can be observed in the microstructure of the alloy in the unstable regions. This is a potential crack and defect formation point. The identified optimum processing parameters are located at (375–450 °C, 0.001–0.03 s−1), with a maximum dissipation efficiency of 0.6. [ABSTRACT FROM AUTHOR]

The present study conducted the isothermal compression of 2024/6061 aluminum alloy bimetallic casting blank using a Gleeble-3500 thermal simulator in the temperature range of 300-450 °C and strain rate range of 0.01-5 s−1 to clarify the interface bonding mechanism. The effect of temperature and strain rate on the stress was studied, and the strain-compensated constitutive model was established. The effects of element diffusion on the interface bonding were clarified. It is found that the stresses decrease with increasing compression temperature and decreasing strain rate. The stress softening behavior is attributed to the combined effect of strain hardening and dynamic softening. The material constants in constitutive model considering compensation of strain are calculated, and the modified constitutive model reflects a relative low predictability of the interface bonding behavior. The sub-grains with low-angle grain boundaries are transformed into the recrystallized grains with high-angle grain boundaries due to the DRX in the bonding interface. The interface recrystallized grains and microstructural reconstitution are the main interface bonding behavior. The diffusion of interface elements is accelerated and the width of bonding layer increases with increasing compression temperature and decreasing strain rate. The continuous distribution of element diffusion in the bonding interface is enhanced. The interface bonding mechanism of the bimetallic blank is mainly characterized by a metallurgical bonding effect. [ABSTRACT FROM AUTHOR]

This study evaluated dry-in-place lubricants used for cold forging. A group of isothermal compression tests with a strain rate ( ε ˙ ) range of 0.001–1 s−1 and temperature (T) range of 30–400 °C were completed. The flow stress (σ) curves of annealed steel S45C were obtained, and a corresponding Hensel—Spittel model was developed to support finite element (FE) simulation. The sensitivity of the steady combined forward and backward extrusion (SCFBE) test proposed in another study was improved by approximately 20% after it was optimized using the results of the FE simulations. Key parameters were identified, and the calibration curves after optimization were obtained. On the basis of the optimized test, a friction testing setup with a heating system was developed, in which the die temperature could be adjusted from room temperature (RT) to 230 °C. Three dry-in-place lubricants and conventional phosphating lubricant were tested, and the friction factors (m), forming loads, and ejection loads were measured. The surface features of the specimens after testing were also investigated. According to the testing results, of the three tested dry-in-place lubricants, the mica type was the best. In addition, the optimized friction testing design was verified as effective. [ABSTRACT FROM AUTHOR]

To investigate the plastic deformation behavior of 18CrNi4A steel at high temperatures, an isothermal hot compression test was conducted on a Thermecmastor-Z series test machine at deformation temperatures from 1273   K to 1423   K and strain rates ranging from 0.01   s − 1 to 10   s − 1 . The effects of these two factors on the flow stress were analyzed. Based on the true stress–strain experimental curves, the original Johnson–Cook constitutive model was applied to determine the flow stress data under different deformation conditions. The prediction results of the model were compared with the experimental data. The main reason for the large deviation observed between them was that the coupling relationship between the deformation temperature and the strain rate was not considered, so the original Johnson–Cook model was modified. The correlation coefficient and average absolute relative error of the original Johnson–Cook model were 0.962 and 16.36%. The prediction accuracy of the modified Johnson–Cook model was improved to 0.991 and 5.58%, respectively. The results show that the modified Johnson–Cook model exhibits higher prediction precision, which is beneficial for the broader application of 18CrNi4A steel in the industry. [ABSTRACT FROM AUTHOR]

SiC particle (SiCp) size has been found to significantly influence the hot workability of particle-reinforced aluminum matrix composites (AMC). In this work, therefore, three types of SiCp/6013 composites with different SiCp sizes (0.7, 5 and 15 μm) were prepared and then subjected to isothermal hot compression tests. In addition, constitutive analysis, processing maps and microstructural characterizations were used to reveal the influence of SiCp size on the hot workability of SiCp/6013 composite. The results showed that the values of hot deformation activation energy Q increased with decreasing SiCp size. Specifically, at lower temperatures (e.g., 350 and 400 °C), the highest peak stress was shown in the AMC with SiCp size of 0.7 μm (AMC-0.7), while in the AMC with SiCp size of 5 μm (AMC-5) at higher temperatures (e.g., 450 and 500 °C). This is because a finer SiCp size would lead to stronger dislocation pinning and grain refinement strengthening effects, and such effects would be weakened at higher temperatures. Further, dynamic softening mechanisms were found to transform from dynamic recovery to dynamic recrystallization with increasing SiCp size, and the dynamic recrystallization occurred more easily at higher temperatures and lower strain rates. Consequently, the instability zones of the composites are all mainly located in the deformation region with lower temperature and higher strain rate, and smaller SiCp results in larger instability zones. [ABSTRACT FROM AUTHOR]

A new scheme for isothermal gas compression process implementation using only a cooling liquid as a liquid piston and as cooling liquid injection was developed. Two options of isothermal gas compression process implementation within the framework of the proposed scheme were studied and the theoretical foundations for their calculations were developed. The conducted numerical experiments made it possible to determine the compression process time, the required liquid piston speed for the isothermal compression process implementation for a given amount of the injected liquid, and the required amount of the injected liquid for a given law of liquid piston speed. The numerical experiments confirmed the possibility of isothermal monatomic gas compression process implementation with a high adiabatic coefficient. [ABSTRACT FROM AUTHOR]

The hot deformation behavior and dynamic softening mechanism of 7B50 aluminum alloy were studied via isothermal compression experiments in the range of 320–460 °C/0.001–1.0 s−1. According to the flow curves obtained from the experiments, the flow behavior of this alloy was analyzed, and the Zener–Hollomon (Z) parameter equation was established. The hot processing maps of this alloy were developed based on the dynamic material model, and the optimal hot working region was determined to be 410–460 °C/0.01–0.001 s−1. The electron backscattered diffraction (EBSD) microstructure analysis of the deformed sample shows that the dynamic softening mechanism and microstructure evolution strongly depend on the Z parameter. Meanwhile, a correlation between the dynamic softening mechanism and the lnZ value was established. Dynamic recovery (DRV) was the only softening mechanism during isothermal compression with lnZ ≥ 20. Discontinuous dynamic recrystallization (DDRX) becomes the dominant dynamic recrystallization (DRX) mechanism under deformation conditions of 15 < lnZ < 20. Meanwhile, the size and percentage of DDRXed grains increased with decreasing lnZ values. The geometric dynamic recrystallization (GDRX) mechanism and continuous dynamic recrystallization (CDRX) mechanism coexist under deformation conditions with lnZ ≤ 15. [ABSTRACT FROM AUTHOR]

The deformation behavior of Ti-48Al-2Cr-2Nb alloy with bimodal grain structure was studied using isothermal compression tests in the temperature range of 950-1100 °C and strain rate range of 0.001-0.1 s−1. The results show that the flow stress is greatly affected by the deformation temperature and strain rate, and decreases with decreasing strain rate and increasing temperature. All flow stress curves exhibit single peak characteristics, indicating that DRX is the main softening mechanism. The Arrhenius constitutive equation is established according to the relationship among flow stress data, strain rate and temperature. The activation energy for hot deformation and stress index are determined as 390.543 kJ·mol−1 and 2.573, respectively. According to the theory of dynamic material model, the hot processing maps are constructed and the stability and instability regions are identified. The peak power dissipation occurs in the regions of 960-1025 °C/0.001-0.005 s−1 and 1085-1100 °C/0.001-0.006 s−1, which suggests that these two regions can be regarded as the optimum processing window for the alloy. [ABSTRACT FROM AUTHOR]

To clarify the hot deformation process characteristics of 5 vol.%TiBw/TA15 composites with three-dimensional (3D) meshed structures, isothermal compression experiments are performed at the temperature of 1173–1373 K with strain rates of 0.001–1 s−1. Two criteria (Prasad and Murty) are employed to study the hot workability of the TiBw/TA15 composites. It is found that typical deformation instability defects (flow localization) are observed in the instability domains in the processing maps. The effects of strain rates and deformation temperatures on the microstructure evolution of the composites are also investigated. The flow stress curve is a manifestation of the deformation behavior of the material, which could reflect a part of the deformation behavior. To better understand the relationship between flow stress and hot deformation parameters, the constitutive equations of composites in the different phase regions (α + β region and β region) are established by combining the deformation temperature, strain rates and true strain. The calculation results show that the hot deformation activation energy is 563.487 kJ mol - 1 and 255.084 kJ mol - 1 in the α + β phase region and β single-phase region, respectively. The experimental results could facilitate the understanding of the hot deformation behavior of 5 vol.%TiBw/TA15 composites. [ABSTRACT FROM AUTHOR]

The objective of this research was to improve the forging outcome of peritectic solidifying cast titanium aluminide (TiAl) 4822 alloy (Ti-48Al-2Nb-2Cr at.%) in hot isostatic pressed and homogenised (HH) condition using cyclic induction heat treatment (CHT). This study adds to research around CHT for TiAl alloys by applying industrially relevant induction heating to conduct five heating cycles at the single αphase temperatures (1370 °C) necessary for grain refinement. Two cooling rates were explored in each cycle, air cooling (ACCHT) and controlled furnace-like cooling (FCCHT), without returning to room temperature. Samples were assessed at each stage in terms of their morphologies, lamellar grain size and content, as well as phase and dynamic recrystallised fraction, and subsequent primary and secondary compression behaviour with uniaxial isothermal compression. The FCCHT process resulted in a homogeneously refined fully lamellar microstructure, and ACCHT, in a heterogeneous microstructure consisting of lamellar and feathery γ (γf) at differing fractions across the piece, depending on the cooling rate compared with HH. The results show that CHT improved forging outcomes for both compression stages investigated, resulting in uniform compression samples with higher volumes of dynamic recrystallised material compared with the instability seen with the compression of HH material. [ABSTRACT FROM AUTHOR]

The focus of designing next-generation gasoline engines is to regulate fuel pressure to reduce fuel consumption and improve performance. In the present study, a novel process for manufacturing high-pressure common rail that is based on forging technology was developed. First, 304 stainless steel raw material was tested for isothermal compression deformation by using different strain rates at different temperatures. Then, a corresponding model, which covers a wide temperature range of 800 to 1200 °C, was established to simulate the real forging process of common rail through a comparative analysis of the revised Arrhenius model and modified Hensel–Spittel model. Second, to improve the common rail's anti-intergranular corrosion capability, mechanical strength, and fatigue resistance during use, the microstructure after hot deformation was analyzed, and the volume fraction of δ-ferrite was quantified. Third, the design of the forging process was analyzed through finite element simulation and was then experimentally validated; the common rail forging parts were formed through two-step forging and flash cutting. Then, the heating treatment process after forming was analyzed, and the results revealed that the δ-ferrite content was reduced to 1%. Finally, a manufacturing process for high-pressure common rail was determined. The results indicate that the common rail forgings produced through the aforementioned process had no mixed crystals or coarse grains, and the intergranular corrosion rate was lower than 0.66 g/m2·h. The yield strength was higher than 220 MPa, the tensile strength was greater than 610 MPa, and the elongation was higher than 52%, which supports the rationality of the manufacturing process. [ABSTRACT FROM AUTHOR]

Warm deformation is a plastic-forming process that differs from traditional cold and hot forming techniques. At the macro level, it can effectively reduce the problem of high deformation resistance in cold deformation and improve the surface decarburization issues during the hot deformation process. Microscopically, it has significant advantages in controlling product structure, refining grain size, and enhancing product mechanical properties. The Gleeble-1500D thermal–mechanical physical simulation system was used to conduct isothermal compression tests on GCr15 bearing steel. The tests were conducted at temperatures of 600–1050 °C and strain rates of 0.01–5 s−1. Based on the experimental data, the critical strain model and dynamic recrystallization model for the warm–hot forming of GCr15 bearing steel were established in this paper. The model accuracy is evaluated using statistical indicators such as the correlation coefficient (R). The dynamic recrystallization model exhibits high predictive accuracy, as indicated by an R-value of 0.986. The established dynamic recrystallization model for GCr15 bearing steel was integrated into the Forge® 3.2 numerical simulation software through secondary program development to simulate the compression process of GCr15 warm–hot forming. The dynamic recrystallization fraction was analyzed in various deformation regions. The grain size of the severe deformation zone, small deformation zone, and difficult deformation zone was compared based on simulated compression specimens under the conditions of 1050 °C and 0.1 s−1 with the corresponding grain size obtained with measurement based on metallographic photos; the relative error between the two is 5.75%. This verifies the accuracy of the established dynamic recrystallization and critical strain models for warm–hot deformation of GCr15 bearing steel. These models provide a theoretical basis for the finite element method analysis and microstructure control of the warm–hot forming process in bearing races. [ABSTRACT FROM AUTHOR]

An approach is proposed making it possible to construct the shock adiabats of molecular crystals of nitro compounds based on the data on their isothermal compression. For this purpose, an equation of state for a crystal of pentaerythritol tetranitrate (PETN) was constructed. The employed comparative analysis of the experimental data on the shock-wave compression of a simple PETN crystal with calculations carried out using the proposed approach to converting the isothermal compression pressures to the shock adiabat and the constructed equation of state of the PETN showed that the experimental and calculated pressure values are within the experimental error. [ABSTRACT FROM AUTHOR]

The Portevin–Le Chatelier effect of Cu–2.0Be alloy was investigated using hot isothermal compression at varying strain rates (0.01–10 s−1) and temperature (903–1063 K). An Arrhenius-type constitutive equation was developed, and the average activation was determined. Both strain-rate-sensitive and temperature-sensitive serrations were identified. The stress–strain curve exhibited three types of serrations: type A at high strain rates, type B (mixed A + B) at medium strain rates, and type C at low strain rates. The serration mechanism is mainly affected by the interaction between the velocity of solute atom diffusion and movable dislocations. As the strain rate increases, the dislocations outpace the diffusion speed of the solute atoms, limiting their ability to effectively pin the dislocations, resulting in lower dislocation density and serration amplitude. Moreover, the dynamic phase transformation triggers the formation of nanoscale dispersive β phases, which impede dislocation and cause a rapid increase in the effective stress required for unpinning, leading to the formation of mixed A + B serrations at 1 s−1. [ABSTRACT FROM AUTHOR]

Through isothermal hot compression experiments at various strain rates and temperatures, the thermal deformation behavior of Zn-2.0Cu-0.15Ti alloy is investigated. The Arrhenius-type model is utilized to forecast flow stress behavior. Results show that the Arrhenius-type model accurately reflects the flow behavior in the entire processing region. The dynamic material model (DMM) reveals that the optimal processing region for the hot processing of Zn-2.0Cu-0.15Ti alloy has a maximum efficiency of about 35%, in the temperatures range (493–543 K) and a strain rate range (0.01–0.1 s−1). Microstructure analysis demonstrates that the primary dynamic softening mechanism of Zn-2.0Cu-0.15Ti alloy after hot compression is significantly influenced by temperature and strain rate. At low temperature (423 K) and low strain rate (0.1 s−1), the interaction of dislocations is the primary mechanism for the softening Zn-2.0Cu-0.15Ti alloys. At a strain rate of 1 s−1, the primary mechanism changes to continuous dynamic recrystallization (CDRX). Discontinuous dynamic recrystallization (DDRX) occurs when Zn-2.0Cu-0.15Ti alloy is deformed under the conditions of 523 K/0.1 s−1, while twinning dynamic recrystallization (TDRX) and CDRX are observed when the strain rate is 10 s−1. [ABSTRACT FROM AUTHOR]

The hot deformation behavior of Al-Zn-Mg-Er-Zr alloy was investigated through an isothermal compression experiment at a strain rate ranging from 0.01 to 10 s−1 and temperature ranging from 350 to 500 °C. The constitutive equation of thermal deformation characteristics based on strain was established, and the microstructure (including grain, substructure and dynamic precipitation) under different deformation conditions was analyzed. It is shown that the steady-state flow stress can be described using the hyperbolic sinusoidal constitutive equation with a deformation activation energy of 160.03 kJ/mol. Two kinds of second phases exist in the deformed alloy; one is the η phase, whose size and quantity changes according to the deformation parameters, and the other is spherical Al3(Er, Zr) particles with good thermal stability. Both kinds of particles pin the dislocation. However, with a decrease in strain rate or increase in temperature, η phases coarsen and their density decreases, and their dislocation locking ability is weakened. However, the size of Al3(Er, Zr) particles does not change with the variation in deformation conditions. So, at higher deformation temperatures, Al3(Er, Zr) particles still pin dislocations and thus refine the subgrain and enhance the strength. Compared with the η phase, Al3(Er, Zr) particles are superior for dislocation locking during hot deformation. A strain rate ranging from 0.1 to 1 s−1 and a deformation temperature ranging from 450 to 500 °C form the safest hot working domain in the processing map. [ABSTRACT FROM AUTHOR]

The present paper contains data on the density (ρ) , sound velocity (u) , and specific heat capacity c p of the mixture of N,N-dimethylformamide + 1-butanol (DMF + BuOH) determined in the entire concentration range of solution and in the temperature range (293.15–318.15) K. The analysis of thermodynamic functions such as isobaric molar expansion, isentropic and isothermal molar compression, isobaric and isochoric molar heat capacity, as well as their excess functions (E p , m E , K S , m E , K T , m E , C p ,   m E , C V ,   m E) and also V m E was undertaken. The analysis of changes in the physicochemical quantities was based on consideration of the system in terms of intermolecular interactions and resulting changes in the mixture structure. The results available in the literature were confusing during the analysis and became the reason for our decision to thoroughly examine the system. What is more, for a system whose components are widely used, there is very scarce information in the literature regarding the heat capacity of the tested mixture, which was also achieved and presented in this publication. The conclusions drawn from so many data points allow us to approximate and understand the changes that occur in the structure of the system due to the repeatability and consistency of the obtained results. [ABSTRACT FROM AUTHOR]